Phospholipids, which are basic substances constituting biomembranes, belong to lipids controlling the fundamental living activities, for example, protection of cell tissues, mediation of information, adjustment of material transfer.
In recent years, it has attracted scientific and industrial attraction that various functional substances can be encapsulated in vesicles (or liposomes) consisting of phospholipids capable of forming bilayer membranes. In the field of pharmaceutical science and medicine, for example, it is expected that this phenomenon is applicable to a drug delivery system (DDS).
The present inventors have tried to apply such high-functional lipids to the food industry and they previously succeeded in the development of a cooking oil suffering from no sputtering and having good mold release characteristics as disclosed in JP-A-1-27431 (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
Examples of the industrial application of PA include, furthermore, improvement of dough properties in a baking process as disclosed in JP-A-58-51853, production of an emulsifier comprising PA and a zein complex as disclosed in JP-A-62-204838, application to drugs as disclosed in JP-A-54-105222, JP-A-55-11582, JP-A-56-127308 and JP-A-60-255728, application to cosmetics as disclosed in JP-A-59-27809 and application to chemical products as disclosed in JP-A-53-108503 and JP-A-60-243171. Namely, attempts have been made to use PA in various industrial fields.
A known method for producing PA comprises treating lecithin with ground oilseeds or an oilseed extract. However, the product thus obtained is contaminated with impurities and thus should be purified. Phospholipids including PA and L-PA are commonly purified by column chromatography. In the purification by silicic acid column chromatography, in particular, each component can be eluted and fractionated by varying the polarity of the development solvent. A chloroform/methanol mixture is used as a development solvent for purifying PA and L-PA and these products are separated from each other by changing the polarity of the solvent by varying the mixing ratio. However, there arises a problem of the contamination with impurities and thus the product should be passed through the column several times in order to obtain a specimen of a high purity, which causes some disadvantages including an increase in the amount of the solvent to be used and a decrease in the yield. It is also proposed to separate PA and L-PA by thin layer chromatography and detecting each product with a non-decomposition reagent, followed by scratching and extracting the portion containing PA or L-PA from the plate. However, this method is seemingly ineffective from an industrial viewpoint, since the yield thus achieved is limited.
On the other hand, there has been known that lecithin is specifically effective, compared with a number of other surfactants, in improving the mold-release characteristics of food materials which are liable to undergo heat adhesion (for example, sponge cake dough, egg roll).
Typical examples of commonly employed lecithin, which comprises a phospholipid mixture comprising nitrogen-containing phospholipids (for example, phosphatidylcholine, phosphatidylethanolamine) as the main components, are obtained by extracting or purifying soybean, yolk or the like.
These natural lecithins such as soybean lecithin and yolk lecithin are unstable and undergo browning when heated to 150.degree. C. or above, even in a fat-protected state, thus turning into a dark brown.
The present inventors found out that a fat and oil composition containing 0.1 % by weight or more of phospholipids, from which the nitrogen-containing phospholipids causing the heat coloration had been removed by, for example, an enzymatic treatment, would never undergo heat coloration when used in frizzling foods and have already applied the same for a patent (JP-A-2-27943).
However, a fat and oil composition containing from 0.01 to 30 % by weight of such phospholipids free from any nitrogen-containing phospholipids still suffers from disadvantages that the oil per se is seriously colored when used at a higher temperature for a long period of time (for example, in frying).